Arthritis induces different patterns of bone turnover in the various compartments of juxta-articular bone. Untreated 12-week-old arthritic mice transgenic for human tumor necrosis factor were evaluated for the numbers (a, c, e) and density (b, d, f) of functional osteoclasts by labeling tartrate-resistant phosphatase and osteoblasts by in-situ hybridization for osteocalcin. Three compartments were analyzed by histomorphometry: (a, b) subchondral bone, (c, d) cortical bone channels and (e, f) the endosteal bone surface distant from inflamed areas. Results are presented as numbers of cells per mm bone surface (a, c, e) and the fraction (%) of bone surface covered by cells (b, d, f). *Statistically significant difference, P < 0.05.